1. Field of the Invention
The present invention relates generally to a voltage converter circuit (or voltage limiter) built in a semiconductor chip, and more particularly to a voltage converter circuit that is effective at low power supply voltages, including those near the internal chip voltage.
2. Description of the Related Art
In general, in the case of a semiconductor integrated circuit constituting a memory or microprocessor, the number of elements increases as the integration degree of the semiconductor integrated circuit is raised. However, current consumption increases because higher operation speed is required. Moreover, elements in the semiconductor integrated circuit are miniaturized and their breakdown voltage is lowered. Therefore, it is necessary to lower the power supply voltage as the integration degree is raised.
The power supply voltage is stipulated to a value such as 5, 3.3, or 2.5 V by the JEDEC (Joint Electronic Device Engineering Council--Electronic Industrial Association), and the power supply voltage of each semiconductor integrated circuit is standardized thereby. It is desirable to keep the external power supply voltage at a conventional value for the effective use of conventional design know-how and to efficiently interface with small- and middle-scale devices.
In consideration of the difference, due to miniaturization and decrease of the breakdown voltage of this type of circuit device, between the characteristics of a semiconductor integrated circuit and external characteristics such as the external power supply voltage, an on-chip voltage converter circuit has been studied. The on-chip voltage converter circuit serves as a power supply circuit for supplying a voltage to an internal circuit on the chip that is lower than the external voltage received by the voltage converter circuit, particularly for a large capacity metal-oxide semiconductor field-effect transistor (MOSFET, or MOS) integrated circuit such as a 16 Mbit dynamic random access memory (DRAM).
An example of a conventional voltage converter circuit is a feedback-control-type voltage converter circuit, which comprises a p-channel MOSFET serving as a control transistor for controlling the output or a driving transistor whose source is connected to the power supply terminal and whose drain is connected to the output terminal, and a MOS differential amplifier that has a signal stage and serves as an error amplifier for comparing the output voltage from the driving transistor with a reference voltage. The differential amplifier controls the driving transistor in accordance with the comparison output. The voltage converter circuit is illustrated in FIG. 4.29 on p. 271 of VLSI Memory, published by BAIFUKAN (transliterated) in November, 1994, and also described in the IEEE Journal of Solid State Circuits, Vol. 23, No. 5, (October. 1988), pp. 1128-1132.